Pontiac Q&A

2001 Pontiac Grand Prix Question: help with my a/c!

2001 pontiac grand prix 3.8 w/170k miles...turn the a/c on and the car clicks (sounds like something is clicking on an off repeatedly) while clicking my rpms start jumping up and down from 300 to 1500 and the a/c stops blowing cold and blows out fire hot air instead of cold